Prabir sat on the stool beside her. ‘Something?’ This was absurd, she had to be mistaken, but he was hardly equipped to tell her where she’d gone wrong in her analysis. ‘What are you suggesting? There’s a retrovirus on the loose that splices a set of fruit pigeon genesinto anything it infects—including some genes that happen to be exactly what fruit pigeons need to vanish into the foliage?’

Grant scowled. ‘I haven’t taken leave of my senses completely. And I don’t have viruses on the brain like you do.’

‘OK, I’ll shut up about viruses. But what’s doing it then? Where did these genes come from?’

She stared down at the bench, still angry with him. He was sure she had an answer, though; she just wasn’t willing to commit it to words.

Prabir said gently, ‘I know how important it is for you to be cautious. But I’m not going to leak your theory to Nature, or sell your data to some rival pharmaceuticals company. And if I’m at risk of fathering children with bright-green feathers, don’t you think I deserve to be told?’

He regretted the words as soon as they were out, but Grant’s expression softened. She said, ‘If these pigeons haven’t interbred for hundreds of thousands of years, what do they still have in common?’

Prabir shrugged. ‘They share the same habitat.’

‘And?’

‘I don’t know. I suppose they’d still share most of their genes, dating back to their last common ancestor.’

Grant said, ‘Exactly. But not just working genes: whole stretches of inactive DNA as well. Don’t you see? That has to be the source of all these “innovations”—they’re not innovations at all! You can’t get functional genes appearing out of nowhere in two or three generations. You just can’t! A random sequence of amino acids doesn’t merely form a useless protein, it forms an ill-conditioned one: a molecule that doesn’t even fold predictably into a well-defined shape. These blood proteins are perfectly conditioned: they have conformations with energy troughs as sharp as haemoglobin’s. The same with the pigmentation morphogenesis proteins that produce the camouflage. The odds of that happening by chance— de novo, in the time frame we’re talking about—are nil.

‘Somehow, these birds must have repaired and reactivated genes from an old common ancestor. They’ve reached back into the archives and dusted off blueprints that haven’t been used for a million years.’ She shook her head, smiling slightly, shocked at her own audacity but triumphant too. ‘That’s what I half suspected all along, but this makes the case a whole lot clearer.’

Prabir was still catching up. ‘You’re saying that all these different species of pigeon have found a way to resurrect fossil genes buried in their DNA, and because they have so much old baggage in common, the same traits have emerged in all of them?’

‘That’s right.’

‘So they’ve all reverted to the appearance of an ancestral species that needed camouflage to hide from some ferocious predator? And presumably they’ve not only lost their flashy plumage, they’ve lost the need for their mates to have it as a prerequisite for sex, or they would have all died out by now?’

‘Presumably, yes.’

‘And when a tree frog or a bat does the same thing with its DNA, the result is different, but still useful, because they’re getting back something that was useful a few million years ago to some frog or bat then?’

‘Yes. That’s the theory.’

Prabir ran a hand over his face; he’d forgotten how tired he was, but after nine hours of slogging through the plantation his brain had turned to mush. ‘That much I follow. Now explain the next part to me, slowly: why is this happening in all these different species? And how?’

Grant hesitated, as if she was about to draw the line here, but then she must have decided that she had nothing more to lose. She said, ‘The only reason I can think of for an innate capacity to do this would be as a response to genetic damage. No one’s ever seen a repair mechanism that operates like this before, but it’s been known for years that functioning genes are vulnerable to certain kinds of damage that leave other parts of the chromosome untouched. Cleaning up old sequences that have fallen into disuse could be a repair strategy of last resort, because even the random copying errors they’ve suffered over time might have done less harm than whatever’s afflicting the modern genes.’

Prabir didn’t dare say it, but this sounded so much like restoring a computer in extremisfrom mothballed backups that it was uncanny. It also sounded so far beyond any conventional notion of how genomes were organised that Grant’s initial refusal to discuss her hypothesis, which he’d taken as verging on paranoia, now looked like mere self-preservation.

‘And that might be handy in somatic cells, to stop certain kinds of cancer?’ he suggested. ‘If some growth regulator gene has been damaged in a cell in my intestine, say, the cell might reactivate a copy of the gene that was duplicated accidentally thousands of generations ago, and fell into disuse?’

‘Exactly. So normally there’d be no visible effects: if an adult starts producing an archaic protein in a few intestinal cells, or skin cells, that’s not going to change its gross anatomy. And even if the process was activated in an early embryo, it would generally produce just one altered individual who’d bear perfectly normal offspring. To produce heritable changes, it has to be turned on in the germ cells; that must be what’s happening here, but don’t ask me why, because I have no idea yet.’

‘OK. But if this is a response to genetic damage, what’s triggering it? Doesn’t there still need to be some kind of powerful mutagen, even if what we’re seeing is the result of the animals conquering it, rather than succumbing to it?’

‘Maybe. Unless it’s being triggered inappropriately; unless they’re overreacting to some other kind of stress.’ Grant lifted her notepad off the bench and thumbed through the sequence of codons. ‘I don’t have all the answers; I’m not even close. The only way to understand this will be to unravel the whole mechanism: identify the genes that are being switched on in every affected species, then see what proteins they encode, what functions they perform, and what activates them in the first place.’

Prabir groaned. ‘ “Every affected species” Why don’t I like the sound of that part?’

Grant regarded him with sergeant-majorly contempt. ‘A bit more field work isn’t going to kill you. You’ve got nothing to complain about; just wait until you get to my age.’

‘You wait until you’ve spent ten years behind a desk.’

She shuddered. ‘All the more reason to want to be here instead. Besides, these are the creatures you grew up with, aren’t they? Think of it as a chance to be reunited with all your old childhood friends.’

‘“Childhood friends’” Prabir climbed off the stool and limped across the cabin to the galley. ‘Do you mean Bambi and Godzilla? Or their mutual great-great-grandparents?’

Prabir slept on deck again, untroubled by insomnia. He woke at first light, aching all over, but unaccountably happier than he’d felt in months.

He dived into the harbour and swam slow laps to a navigation buoy and back, just to loosen the muscles in his shoulders. People heading out in rickety fishing boats shouted greetings, and in the water the close heat of dawn didn’t feel oppressive at all. He’d taken up swimming in Toronto for a while, doing laps before work in a pool full of fanatics with scalp-to-toe anti-turbulence depilation and sports watches with faux-AI plug-ins to coach them on their stroke. But it had made him feel twice as tense as doing nothing, so he’d given it away.

Thinking back on the evening’s revelations, his sunny mood seemed less of a mystery. Even if Grant’s theory turned out to be misguided, one way or another the data they collected would help shed light on what was happening. That wasn’t exactly what had brought him here, but the more he thought about it, the more it seemed like the key to all his anxieties. Ever since Madhusree had told him about the expedition, he’d been treating the spread of the mutations as some kind of vague malevolent force, reaching out from Teranesia to drag her back into its clutches, mocking the very idea that they’d ever escaped. That was every bit as deranged as anything the cranks in Ambon had spouted, but the clearer the real, molecular basis for the effect became, the harder it would be to sustain that kind of delusion. A complete answer might be decades away, but playing some small part in getting there would make him feel less helpless, less overwhelmed. That was what his parents had spent their lives fighting for: not just explaining the butterflies, but puncturing the whole deeply corrupting illusion that nature—or some surrogate deity—ever had designs on anyone, malevolent or otherwise.